Fiber Reinforced Polymer Plates Research Articles

Durability of FRP-strengthened RC beams subjected to 110 months accelerated laboratory and field exposure

This paper presents an experimental investigation of the long-term performance of fiber reinforced polymer (FRP) composites strengthened reinforced concrete (RC) beams. The beam specimens had identical dimensions. Different FRP composites and adhesives were used, including carbon FRP (CFRP) plate bonded with Sika 30; CFRP plate bonded with Araldite 106; CFRP sheet bonded with SW-3C; and glass FRP (GFRP) bonded with Sika 330. Their performance was tested after 8, 18, 31, and 110 months of exposure to the wet-dry cyclic environment, and 48 and 110 months of exposure to the outdoor environment. Test results show that the FRP-strengthened RC beams subjected to the wet-dry cyclic environment exhibited more significant degradation compared to those subjected to the outdoor environment. In the wet-dry cyclic environment, CFRP plate/Sika 30 strengthened beams and CFRP sheet/SW-3C strengthened beams exhibited better durability performance with only 6 % and 4 % reductions in the flexural capacity after 110 months, respectively. In contrast, CFRP plate/Araldite 106 strengthened beams and GFRP sheet/Sika 330 strengthened beams exhibited larger reductions of 30 % and 31 %, respectively. Furthermore, the FRP debonding strain was reduced over time. A reduction factor is proposed for the design of FRP debonding strain based on test results to ensure long-term safety.

Innovative design and sensing performance of a novel large-strain sensor for prestressed FRP plates

Owing to the low measuring range of traditional fiber Bragg grating (FBG) sensors and the complexity, imprecision, and lack of practicality in existing large-strain sensors, this paper introduces a novel type of large-strain sensor based on pre-relaxation and continuous sensing technology. This design aims to realize the whole-process strain monitoring of prestressed fiber reinforced polymer (FRP) plates. Static tensile tests were conducted on 9 large-strain sensor specimens. The effects of pre-relaxation degree, section number, pre-tension time, and prestressing level were evaluated. The results reveal that, the pre-relaxed sensor, proved its efficacy in capturing the strain pertinent to the post-tensioned operational state of the FRP plate, and a sensing performance of up to 18,923 με can be facilitated and further extended by a pre-relaxation and continuous sensing technique. Moreover, it is recommended that during the fabrication of the large-strain sensor, two pre-tensions be applied, with a prestressing level between 115% and 125% of the pre-relaxation degree.

Array infrared thermography for visualization of defects in bonded fiber reinforced polymer joints

Fiber reinforced polymer (FRP) is widely used in new and existing structures, however, interfacial defects in the bonded joints pose a significant threat to structural integrity. Therefore, detection of interfacial defects is imperative for ensuring structural safety. This study proposes array infrared thermography (IRT) as a novel non-destructive evaluation method to visualize interfacial defects. Array IRT provides uniform heat excitation within the spatial domain, which overcomes the problem of heat concentration by conventional IRT. Forty-five bonded FRP plate specimens were tested using array IRT, results of which show that interfacial defects can be accurately detected within (8h + 8) s (where h is the thickness of the upper layer of FRP in mm). Array IRT achieves high accuracy in detecting shapes, particularly sharp corners of defects. A pre-processing method was proposed to eliminate the twisted angles of thermal camera and to more clearly show the defects in the thermograms. A database containing tested thermograms and the corresponding predefined defects was established. Intelligent algorithms - UNet, Deeplabv3, and YOLOv8 - were used to segment the defected regions for array IRT analysis, results of which show a precision of 95.8 %, 94.4 %, and 94.1 %, respectively.

Adaptation of an Eddy Current Model for Characterizing Subsurface Defects in CFRP Plates Using FEM Analysis Based on Energy Functional

In this work, a known Eddy Current (EC) model is adapted to characterize subsurface defects in carbon fiber-reinforced polymer (CFRP) plates intended for the civil aerospace industry. The considered defects include delaminations, microcracks, porosity, fiber breakage, and the simultaneous presence of these defects. Each defect is modeled as an additive variation in the material’s electrical conductivity tensor, allowing for a detailed mathematical representation of the defect’s influence on the CFRP’s electromagnetic behavior. The additivity of the variations in the conductivity tensor is justified by the assumption that the defects are not visible to the naked eye, implying that the material does not require non-destructive testing. The adapted EC model admits a unique and stable solution by verifying that all analytical steps are satisfied. To reconstruct 2D maps of the magnetic flux density amplitude, a FEM formulation is adopted, based on the energy functional because it ensures a stable and consistent numerical formulation given its coercivity. Moreover, the numerical approach allows precise and reliable numerical solutions, enhancing the capability to detect and quantify defects. The numerical results show that the obtained 2D maps are entirely superimposable on those highlighting the distribution of mechanical stress states known in the literature, offering a clear advantage in terms of detection costs. This approach provides an effective and economical solution for the non-destructive inspection of CFRP, ensuring accurate and timely defect diagnosis for maintaining structural integrity.

Effect of adhesive ductility on the bond behavior of CFRP-steel cohesive interfaces made with toughened epoxy resin

The strengthening of steel structures can be effectively performed using carbon fiber-reinforced polymers (CFRP) plates. Specifically, the behavior of corroded and fatigue damaged steel bridges can be significantly improved using externally bonded (EB) or unbonded composite reinforcements. For bonded composites, the bond between the reinforcement and the steel substrate is the weak link of the system. Indeed, cohesive failure within the adhesive layer represents the main failure mode, which makes the selection of a proper adhesive fundamental to achieve an improvement of the system load carrying capacity and fatigue resistance. Within this context, the use of toughened adhesives represents a promising solution. However, research regarding these adhesives is still limited. In this paper, 18 single-lap direct shear tests are performed to evaluate the cohesive behavior of toughened and traditional adhesives. For some specimens, the full-range bond behavior, including the load response snap-back, was experimentally captured. The digital image correlation (DIC) technique is adopted to evaluate the adhesives cohesive material law (CML). The effect of adhesive ductility, plate stiffness, and bonded length on the joint load response is investigated. Finally, experimental results are validated and discussed against the analytical predictions of a cohesive model based on a trapezoidal CML.

A fiber optic laser-ultrasonic transmitter based on collapsed photonic crystal fiber for ultrasonic testing

Ultrasonic testing technology is widely used for its exceptional accuracy and resolution. Commercial ultrasonic testing systems basically use piezoelectric transducers as ultrasonic excitation elements. However, the performance of piezoelectric transducers is not stable enough in high-temperature and high-humidity environments. Therefore, a fiber optic laser-ultrasonic transmitter based on collapsed photonic crystal fiber (CPCF) was proposed. The CPCF guides the laser in the core into the photoacoustic material and realizes the ultrasonic excitation on the side wall of the fiber based on the optical-thermal-acoustic energy conversion. Finite element analysis and experimental research on the photonic crystal fiber (PCF)-CPCF-PCF microstructure show that controlling the CPCF length precisely enables quantitative modulation of the optical coupling coefficient, reflecting the optical energy in photoacoustic energy conversion. Three PCF-CPCF-PCF microstructures with different optical coupling coefficients were fusion spliced onto an optical fiber, and three-point ultrasonic excitation was successfully achieved on aluminum plates. The peak-to-peak values are all around 1.5 V, indicating that the energy of ultrasonic waves is balanced, which helps realize the baseline-free and standardized application of transmitters. Furthermore, the detection effect of ultrasonic waves generated by the transmitter on the thickness and defects of the plate was studied. By analyzing the ultrasonic echoes in the aluminum and carbon fiber-reinforced polymer plates, the corresponding wave speeds were calculated to be 6030.52 and 2522.34 m/s, similar to the longitudinal wave speeds in the corresponding materials. The indicators of ultrasonic waves in the time domain and frequency domain are sensitive to the thickness and defects of the plate. The amplitude and time-of-flight of the ultrasonic wave change monotonically with increasing damage severity. This study elucidates the principle of the fiber optic ultrasonic transmitter and demonstrates its capability of quasi-distributed ultrasonic excitation. Furthermore, the feasibility of non-destructive testing based on this transmitter was also verified.

Analysis of damage evolution in single‐lap and double‐lap bolted joints of carbon fiber reinforced polymer plates based on load distribution

AbstractIt is important to study damage evolution as well as failure of carbon fiber reinforced polymer (CFRP) plates bolted joints. Therefore, the quasi‐static tensile test on single‐lap and double‐lap CFRP plates bolted joints was conducted. Meanwhile, the tensile strength prediction model for titanium alloy bolted joint of CFRP plates was established based on the improved 3D Hashin failure criterion, then a theoretical model was proposed to accurately predict the load distributions and tilt angle of bolted joints. Thus, the load–displacement curves were divided into four stages, and load distributions at different stage points as well as the relationship between tilt angle of bolt and load variation were obtained. The damage evolution of single‐lap and double‐lap at different stage points was analyzed respectively, and failure mechanisms were revealed based on load distribution. The results show that the ultimate failure of single‐lap is caused by the intrusion of bolt head into CFRP plates, while double‐lap is caused by the compression deformation of central plate. The numerical simulation works are in high agreement with the experimental results.Highlights Calculate the load distribution at single‐lap and double‐lap bolted joints. Obtain the relationship between bolts tilt angle and load variation. Analysis of damage evolution in bolt‐hole wall of carbon fiber reinforced polymer (CFRP) plates. Using loads to reveal the failure mechanisms of single‐lap and double‐lap bolted joints of CFRP plates.

Flexural Behavior Evaluation for Seismic, Durability and Structure Performance Improvement of Aged Bridge According to Reinforcement Methods

Among infrastructure, concrete bridges are the most exposed to various environmental effects. Structural degradation occurs due to natural and artificial influences shortening the lifespan of the structure. Therefore, bridges need to be reinforced over time. The structures used in this study are re-formed using aged bridge floor decks that have been used for 50 years, approximately. The fiber-reinforced polymer (FRP) adhesion method, using sheets and plate forms, was selected among various reinforcement methods to investigate the performance of reinforced structures. We have tested various reinforcement scenarios including one and two layers FRP sheets and FRP plates. The mechanical properties of the reinforced structures were evaluated experimentally through tensile strength and flexural test experiments. In contrast to most available literature focused on model-based studies, our present work represents an experimental test validation of structural reinforcement on an actual bridge. Our results indicate that fiber-based reinforcement in sheet form exhibits higher performances of the reinforced structure compared to reinforcement using the plate form. This study is intended to provide sufficient data for reinforcing bridge floors that could be used for reference at future construction sites.

Evaluating impact damage on carbon fiber-reinforced polymer plates utilizing zero-group-velocity Lamb waves

This paper presents an effective method for evaluating the impact damage of composite plates using zero-group-velocity (ZGV) Lamb waves. A finite element (FE) model of the carbon fiber-reinforced polymer (CFRP) plate is established to analyze in detail the propagation characteristics of the S1-ZGV Lamb wave mode with a specified propagation direction. The study investigates the changes in the S1-ZGV mode with varying damage levels, characterized by a decrease in elastic moduli. Results indicate that as the damage level increases, the corresponding S1-ZGV frequency and amplitude decrease proportionally. The spectral amplitude (SA) at the initial S1-ZGV frequency exhibits a consistent and significant decrease with increasing damage levels, offering a reliable method for accurately assessing damage in CFRP plates. Additionally, the S1-ZGV mode of the CFRP plate is experimentally excited using the pitch-catch technique with air-coupled ultrasonic transducers to explore the variations in the S1-ZGV mode with different impact damages. Experimental findings show that the SA of the S1-ZGV mode at the initial S1-ZGV frequency decreases monotonically and sensitively with an increasing number of impacts. These experimental results correlate with the FE analysis, validating the effectiveness of accurately evaluating impact damage in CFRP plates based on the SA of S1-ZGV modes.

Prestressed CFRP Plates and Tendon Strengthening of Steel–Concrete Composite Beams

This study aims to enhance the ultimate capacity and stiffness of steel–concrete composite beams through external strengthening with prestressed carbon fiber-reinforced polymer (CFRP) plates and post-tensioned CFRP tendons. A 3D finite element model was developed using ANSYS and validated using experiments. The impact of various parameters on the capacity of the beam was investigated, including the level of post-tensioning in the CFRP tendons, tendon profile, degree of shear connection, and beam load level when adding strengthening CFRP tendons. Results indicate that reinforcing composite beams with bonded CFRP plates using post-tensioning tendons with trapezoidal and parabolic profiles can increase maximum load capacity by 37% and 60%, respectively, while maintaining high stiffness. This study also indicates that the optimal strengthening conditions for the composite beam are when the beam is loaded up to 70% of its capacity and has a composite action degree of 100%.

Behavior of steel plate shear walls reinforced with stiffened FRP plates

Steel plate shear walls require retrofitting due to factors such as corrosion, long–term loading and functional changes. In an effort to modernise the technology used for strengthening and retrofitting steel plate shear walls, fibre–reinforced polymer (FRP) plates with additional stiffeners are employed to enhance the shear capacity of steel structures. In this study, the static properties of steel plates reinforced with these stiffened FRP plates were experimentally investigated. The application of this strengthening methodology substantially enhanced the out–of–plane stability, shear stiffness and bearing capacity of the plates, while also reducing fatigue damage. Equations for estimating the buckling and ultimate load of steel plates reinforced with stiffened FRP plates have been derived, enabling predictions of their practical performance. Finite element models incorporating the potential failure of epoxy at the FRP–steel interface were developed for further analysis. A numerical study was performed to investigate the optimal thickness of the FRP stiffener. The analysis revealed that stiffener thicknesses exceeding 6 mm did not significantly contribute to the enhancement of the load–bearing capacity or to the prevention of debonding. When the FRP rib thickness exceeds 6 mm, the economy was poor. The aforementioned findings are of considerable engineering importance, especially in the context of improving fatigue properties and shear load–bearing capacity of thin steel plates.

Bending performance of laminated veneer lumber timber beams strengthened in the compression side with near-surface mounted CFRP plates

This study investigated the bending behavior of timber beams that were strengthened using carbon fiber-reinforced polymer (CFRP) plates. Fourteen laminated veneer lumber (LVL) timber beams, each measuring 60 mm×200 mm x 2400 mm, were subjected to four-point bending tests. The objective was to investigate the effect of using CFRP plates as near-surface mounted (NSM) strengthening in the compression zone on the bending behavior of the LVL timber beams. In this experiment, two beams were left unstrengthened while the remaining beams were strengthened with varying lengths, depths and numbers of CFRP plates. The beams load-midspan deflection relationship, ultimate load capacity, stiffness, failure mode, and strain profile distribution were analysed based on experimental results. The use of CFRP plates in the compression zone of LVL beams has been found to improve their strength and stiffness. The test result showed timber beams strengthened with CFRP plates with a reinforcement ratio ranging from 1.67 % to 5.00 % experienced a significant increase in bending strength of 4.24–28.85 % and an increase in bending stiffness of 16.48–62.51 %. These results indicate that NSM CFRP plates can effectively strengthen timber materials, offering improved bending performance and durability.

Anchoring and stressing methods for prestressed FRP plates: State-of-the-art review

Prestressing of the fiber-reinforced polymer (FRP) plate is applied to fully extend the high-strength performance of the FRP plate in structure reinforcement. Anchoring methods and stressing are the two main issues for prestressed FRP plates. Although a number of methods concerning those two main issues have been developed, the literature lacks a systematic review on the existing methods for FRP plates anchoring and stressing. This article compares the comprehensive performance of different FRP plates, recommending BFRP plates as more suitable for use in prestressed tensioning systems. It contrasts the principles and applicability of various anchoring devices, suggesting that wedge-type clip anchors and flat-type anchors show promising development prospects. Additionally, addressing stress concentration in the anchorage zones of low-modulus FRP plates is key to enhancing anchoring efficiency. Ultimately, the paper evaluates tensioning methods for FRP plates, identifying “the method of jacking against the strengthened component” as the most promising, yet it requires innovation in terms of dimensions and positioning of the tensioning frame to enhance its applicability to specific engineering needs.

Modeling and analysis of acoustoelastic guided waves propagation in anisotropic fiber reinforced polymer composite plates under initial gradient stress

Process-induced initial gradient stress is inevitable during the fabrication of fiber reinforced polymer (FRP) composites. In this research, governing wave equations with variable coefficients are established for FRP plates under initial gradient stress, based on the acoustoelastic theories. The Legendre polynomial (LP) method is utilized to derive the solving algorithm. The dispersion curves are obtained without layer slicing, which provides a more realistic analysis model for gradient stress. The accuracy and convergence of the proposed method are discussed through numerical examples. The influences of initial gradient stress on dispersion slowness curves of Lamb and SH waves are analyzed, considering the parabolic initial gradient stress distribution, in which it’s common in the manufacturing process of FRP composites. The effect of initial gradient stress distribution on the phase velocity is investigated in detail. The influence of the anisotropic effect of FRP on guided wave propagation under initial gradient stress is discussed. The numerical analysis shows that the behavior of guided waves is influenced not only by the initial gradient stress but also dominated by propagation direction in anisotropic FRP composite plates. These results can provide a useful reference for the testing based on guided waves for FRP composite, especially when the initial gradient stress is encountered.

Dynamic properties of natural fiber-reinforced polymer composite plates and tubes

Thirty-six flax fibre-reinforced epoxy (FFRE) plates with two, three, and four fabric layers and lengths ranging from 160 mm to 270 mm and nine FFRE tubes with a diameter of 60 mm, a length of six times the tube diameter plus an overly of 50 mm with two, three, and four fabric layers were manufactured. One-hundred-eighty impulse excitation tests were conducted on FFRE plates to determine the dynamic properties of the plates in the bending mode, and 91 impulse excitation tests were conducted on the FFRE tubes to determine the dynamic properties of the tubes in the transverse, torsional, and longitudinal directions. FFRE plates showed up to six times larger specific energy capacities compared to counterpart glass fibre-reinforced polymer plates, showing significant potential for FFRE plates to replace the use of GFRP plates where considerable damping of energy is required. The results showed that the damping ratio of the FFRE plates decreased with the increase in layers and natural frequency. For the FFRE tubes, the highest damping ratio belonged to the transverse vibration mode, followed by the torsional or longitudinal vibration modes.

Damage detection of thin plates by fusing variational mode decomposition and spectral entropy

This paper presents a new approach for damage detection in thin plates by fusing variational mode decomposition and spectral entropy (VMD-SE). In this method, after the received signal is decomposed into some intrinsic mode functions (IMFs) by variational mode decomposition (VMD), the spectral entropy ratio of the first and last IMFs is calculated for optimizing the VMD’s parameters and improving its decomposition performance. Moreover, the cross-correlation coefficient between the decomposed IMFs and the reference signal is computed to separate the desired IMF, which contains more damage information. Finally, the spectral entropy of the obtained IMF is calculated as an indicator for assessing the damage’s severity. The comparative analysis of the simulated signal clearly shows that only the proposed method can successfully separate the damage-related and reference signals. To verify the VMD-SE method, damage detection of two different types of damage on aluminum and composite fiber-reinforced polymer (CFRP) plates is conducted by using this new approach. The experimental results demonstrate that the parameters of VMD affect greatly its decomposition performance, and the best parameters are selected. The results also indicate that the normalized spectral entropy monotonically increases when the diameter of the through-hole or the length of the scratch increases. In addition, the correlation coefficients of the fitting lines of the plates are larger than 0.998. The experimental results of aluminum specimens demonstrate that the damage’s location has an influence on the normalized spectral entropy. At last, based on the linear relationship, the severity of damage in the fourth specimen is identified. The identification results demonstrate that the relative error of the aluminum and CFRP plates is less than 7.34%, which indicates that this new algorithm by fusing VMD and spectral entropy can detect the damage size in thin plates accurately and efficiently.

Measuring the in-plane thermal diffusivity of anisotropic solids by lock-in infrared thermography: Laser-spot vs laser-line heating

A method is proposed to measure the in-plane thermal diffusivity of anisotropic solids along an arbitrary direction using laser-line lock-in thermography. In this method, the sample is heated by an intensity-modulated laser beam, which impinges on the sample surface with the shape of a narrow strip. The resulting temperature oscillations are recorded by a thermographic camera and a phase thermogram is obtained by lock-in processing the image sequence. The thermal diffusivity along the direction perpendicular to the laser line can be determined from the linear dependence of phase lag with the distance to the heating line using the slope method. Unlike laser-spot lock-in thermography, in which the slope method only provides the thermal diffusivity along the principal directions, in this configuration, the thermal diffusivity can be measured experimentally along any direction, just selecting the relative orientation of the sample with respect to the laser line. Moreover, this configuration allows averaging several parallel phase profiles leading to more reliable thermal diffusivity values. The experimental results are presented for a highly anisotropic material, namely, a unidirectional carbon fiber-reinforced polymer plate.

Bond-Damaged Prestressed AASHTO Type III Girder-Deck System with Retrofits: Parametric Study

This research describes an in-depth analysis of the flexural strength of a strengthened AASHTO Type III girder-deck system with debonding-damaged strands based on the finite element software ABAQUS 6.17. To investigate the stand-debonding impact and retrofit, two strengthening techniques by the separate use of carbon fiber-reinforced polymer (CFRP) and steel plate (SP) were proposed. A detailed finite element analysis (FEA) model considering strand debonding, material deterioration, and retrofitting systems was developed and verified against relevant experimental data obtained by other researchers. The proposed FEA model and the experimental data were in good agreement. The sensitivity of the numerical model to the mesh size, element type, dilation angle and coefficient of friction was also investigated. Based on the verified FEA model, 156 girder-deck systems were studied, considering the following variables: (1) debonding level, (2) span-to-depth ratio (L/d), (3) strengthening type, and (4) strengthening material amount. The results indicated that the debonding level and span-to-depth ratio had a major effect on both load–deflection behaviors and the ultimate strength. The relationships between the enhancement of the ultimate strength and the thickness of the strengthening material were obtained through regression equations with respect to the CFRP- and SP-strengthened specimens. The coefficient of determination (R2) was 0.9928 for the CFRP group and 0.9968 for the SP group.

Flexural behaviour of bamboo scrimber beams with different composite and reinforced technology: A literature review

Bamboo scrimber (BS) is a novel renewable biocomposite material with excellent mechanical performance and stability that is suitable for load-bearing structural members. Beam-type components are among the most widely used members in structural engineering, and their flexural behaviour is crucial for the safety and applicability of structures. Based on a review of the existing literature, this article presents a comprehensive overview and discussion of the research and development of various forms of beam-type BS members with the aim of reaching a clearer understanding of the bending mechanisms and mechanical characteristics of BS beams. The members highlighted in this review include general BS beams, reinforced BS beams (with steel bars and fibre-reinforced polymer plates), composite BS beams (with profile steel and concrete), and strengthened damaged BS beams. Moreover, the factors affecting the flexural performance of BS beams, such as span-depth ratios, their mechanical properties, and reinforcing materials, are analysed quantitatively. Finally, the calculation models for the flexural bearing capacity and stiffness of BS beams are summarised and compared. This review aims to illustrate the potential of BS in the field of structural engineering and provide references for future research and design methods for BS flexural members.

Fracture research of adhesive-bonded joints for GFRP laminates under mixed-mode loading condition

Abstract The mixed-mode fracture characterization of adhesively bonded glass fiber-reinforced polymer (GFRP) plate joints is studied based on theoretical and experimental techniques. An improved beam model is used to estimate the compliance and the mixed-mode energy release rate (ERR) for GFRP four-point mixed-mode bending specimens. In this model, the deformation of the upper and lower GFRP plates is mutually independent, and the deformable adhesive is considered to satisfy the displacement compatibility conditions on the bonding interface. The explicit theoretical solutions of the compliance and ERR using the compliance method are reduced. The present theoretical solutions fit well with the finite element solutions by comparison with the rigid joint model. From the critical loads in experiment, the variation in fracture toughness on mixed-mode I/II has been determined by modifying the stiffness of the composite GFRP/GFRP substrate.